Heat Exchanger

ABSTRACT

A heat exchanger for an automotive vehicle comprises a tank and a beam of tubes, received at their extremities in openings of the tank where the tubes are linked to the tank through tube to tank junctions. Some of the tube to tank junctions suffer thermal stress. At least some of the tubes involved in the tube to tank junctions suffering thermal stress have a higher mechanical resistance than the other tubes.

The invention concerns heat exchangers, and particularly heat exchangersfor the automobile industry.

Typically, heat exchangers for automotive vehicles comprise a beam oftubes for circulating a heat exchange fluid, between two boxes alsocalled tanks or collectors. The challenge in the design of heatexchangers is based on making the right trade-offs to ensure the bestperformance/packaging/endurance ratio.

This is particularly the case in the field of double heat exchangers,where a first part of the radiator circulates a heat exchange fluid at afirst, high temperature, and a second part of the radiator circulatesthe heat exchange fluid (or another one) at a second, low temperature.

This type of radiator has many packaging advantages, yet their design ischallenging, because they are subject to high stress in the region ofseparation between the high temperature region and the low temperatureregion.

However, as the designs of the heat exchangers have improved, issuesrelating to local stress have spread to regular heat exchangers, havingsingle or multiple passes, as their dimensions where increasinglyreduced to accommodate smaller packaging and lower weight.

Many designs have been tried to deal with these problems:

-   -   use of two neighboring baffles in both tanks, thereby generating        dead tubes, and in which tightness of the tanks is hard to        ensure, and tank assembly process is complicated,    -   use of tank profile modification, by brazing the collector and        the header forming the tank to provide a baffle, which        complicates the tank assembly,    -   use of a region separating baffle in both tanks, jointly with        corks in the adjoining tubes, in order to reduce the flow in        these regions, which among other drawbacks greatly complicates        the radiator and tank assembly,    -   use of a region separating baffle in both tanks, the baffle also        covering several tubes to provide dead tubes, and being        complemented with tightness gaskets, which an expansive solution        with a complicated assembly,    -   use of inserts for creating dead tubes, which greatly        complicates the assembly, etc.

It is obvious from the mere length of the above list that nosatisfactory solution has been found so far to provide a good localreinforcement of the tank/tube junction while limiting pressure drop,cost increase and assembly complication.

The invention improves this situation.

To meet this goal, the invention proposes a heat exchanger for anautomotive vehicle, comprising a tank and a beam of tubes, received attheir extremities in openings of said tank where said tubes are linkedto said tank through tube to tank junctions, some of said tube to tankjunctions suffering thermal stress characterized in that at least someof the tubes involved in said tube to tank junctions suffering thermalstress have a higher mechanical resistance than the other tubes.

According to the invention, the mechanical resistance of the heatexchanger is thus enhanced in the areas suffering thermal stress by thetubes themselves. And the risk of failure due to thermal stress islowered without additional parts or complicated designs. Pressure dropincrease is also limited.

Preferably, said tubes having higher mechanical resistance are extrudedtubes and said other tubes are folded tubes.

Other characteristics and advantages of the invention will appear fromthe following description of drawings, given by way of example and in anon limitative way.

In the drawings:

FIG. 1 shows a schematic view of a heat exchanger according to theinvention,

FIG. 2 shows a schematic cross-sectional view of a locally reinforcedregion of the heat exchanger of FIG. 1,

FIG. 3 shows a top view of the region of FIG. 2,

FIGS. 4 and 5 show two further embodiments of a heat exchanger accordingto the invention, and

FIG. 6 shows a schematic cross-sectional view of a locally reinforcedregion of the heat exchanger of FIGS. 4 and 5.

The drawings and the following description essentially comprise elementshaving a defining character. Thus, they may serve to enhance thecomprehension of the invention, but also to help defining it, in somecases.

FIG. 1 shows a schematic view of a heat exchanger 2 according to theinvention. Heat exchanger 2 is a single pass radiator for air cooling,which comprises tanks 4 and 5 and a beam 6 comprised of tubes 8.

As appears on FIG. 2, tanks 4 and 5 each comprise a cover 10 received ina collector 12. Tank 4 comprises a heat exchange fluid input 14, andtank 5 comprises a heat exchange fluid output 16.

The beam 6 is made of tubes 8 which are generally long, and parallelbetween them. Each tube 8 is received in a respective opening of tanks 4and 6. Between tubes 8, fins are arranged, which enhance the heatexchange surface, and which are not represented here for simplicity.

The tubes 8 are generally made of aluminium are made by folding of asheet unto itself, thus forming two channels, as can be seen on FIG. 3.Beam 6 comprises specific tubes in regions referenced by the number 18located at the tank end.

In the regions 18, the stress level due to mechanical constraints andtemperature shocks is such that the regular folded tubes 8 may break. Inorder to overcome this problem, the Applicant has found that specifictubes 19 which appear more readily on FIGS. 2 and 3 solves all theresistance issues.

The tubes 19 are made by an extrusion technique. This is particularlyadvantageous, because it allows designing tubes which have a differentcross-section, as well as several ribs for strengthening, for instancetwo or more ribs, defining channels 40 for fluid circulation.

In the example shown on FIG. 2, tube 19 comprises 3 ribs 20, each havinga thickness of 0.35 mm. In various embodiments, the number of ribs maybe comprised between 2 and 12, and preferably is more than 7 and lessthan 12. In various embodiments, the thickness of ribs 20 may be chosenbetween 0.15 mm and 3 mm, and more preferably between 0.2 mm and 1.5 mm

The tube 19 has a radial wall thickness T of 1.5 mm and a transversewall thickness t of 0.35 mm In various embodiments, the radial wallthickness T may be chosen between 0.225 mm and 5 mm, and more preferablybetween 0.75 mm and 3 mm. In various embodiments, the transverse wallthickness t may be chosen between 0.15 mm and 3 mm, and more preferablybetween 0.2 mm and 1.5 mm

In general the radial wall thickness T is chosen to be at least biggerthan 1.5 times that of the transverse wall thickness t. Preferably, thewall thickness ratio is chosen to be at least bigger than 2, and lessthan 10.

The tube 19 resistance in terms of thermal shock elongation andcompression is defined by its number of ribs, their thickness, theradial wall thickness T and the transverse wall thickness t.

The adjustment of the tube parameters will vary according to theapplication which is considered, and the specific heat dissipationsought. However, the wall thickness ratio will remain in the abovementioned ranges.

The cross section of the radial walls of the extruded tubes may becircular as regards the external side thereof and circular and/orelliptic as regards the internal side thereof. In other words, thechannels 40 extending laterally may have a circular and/or elliptic sidewall along the tube lateral sides.

In other embodiments, regions 18 may be further strengthened byproviding more than one tube 19, e.g. 2 to 4 tubes. Since the regions 18are located at the extremity of the tanks, the use of the tubes 19 doesnot complicate the assembly of the heat exchanger.

FIGS. 4 and 5 show two other embodiments according to the invention. Inthose figures, tanks 4 and 6 are similar to those of FIG. 1, but haveadditional elements.

In FIG. 4, tank 4 further comprises a baffle 22 and a further heatexchange fluid input and/or output 24, the heat exchanger thus being atwo-pass heat exchanger. In FIG. 5, tank 5 also further comprises abaffle 26 and a further heat exchange fluid input and/or output 28, theheat exchanger thus forming a double heat exchanger.

The beam of the heat exchangers of FIGS. 4 and 5 show further localstress regions referenced 30. FIG. 6 shows a top view of a region 30,from the inside of tank. In the example shown in FIG. 6, it is theregion 30 of FIG. 4 or 5 which is represented, and baffle 22 is shownaccordingly.

In the region 30, the baffle 22 is arranged between two openings of tank4. Since the heat exchange fluid circulating in the heat exchanger willshow significant difference in temperature, the tubes in the region 30,i.e. the tubes received in the opening neighboring baffle 22, aresubject to a high level of stress, similarly to tubes 19 of regions 18.

In order to address these stress issues, region 30 comprises tubes 32received in the openings which surround baffle 32. While the use of abaffle does complicate the assembly process, no other satisfactorysolution exists to this day. Also, the use of tubes 32 allows betterstress resistance, and ensures tightness of the heat exchanger, thusproviding the best trade-off in terms of assembly and resistance.

The tubes 32 are similar to tubes 19, i.e they are built by an extrusiontechnique. Furthermore, they have identical dimensions in the exampleshown here, and they may be made with dimensions within the previouslydescribed ranges, including the number of ribs.

Also, while the region 30 shown in FIG. 6 comprises only one tube 32 oneach side of baffle 22, it may comprise more than one tube 32 on eachside, e.g. 2 to 4. Further, there may be more tubes 32 on one side ofbaffle 22 than on the other side, e.g. 1 or 2 tubes 32 on one side, and3 or 4 tubes 32 on the other sides.

While the invention above has been described with respect to specificembodiments, it should be understood that they can be combined, and thatthe present specification discloses all of the possible combinations ofthose specific embodiments.

1. A heat exchanger for an automotive vehicle, said heat exchangercomprising a tank and a beam of tubes, received at their extremities inopenings of said tank where said tubes are linked to said tank throughtube to tank junctions, wherein some of said tube to tank junctionssuffer thermal stress, and wherein at least some of the tubes involvedin said tube to tank junctions suffering thermal stress have a highermechanical resistance than the other tubes.
 2. A heat exchangeraccording to claim 1, wherein said tubes having higher mechanicalresistance are extruded tubes and said other tubes are folded tubes. 3.A heat exchanger according to claim 2, wherein said extruded tubes havea radial wall thickness to transverse wall thickness ratio superior orequal to 1.5.
 4. A heat exchanger according to claim 3, wherein saidradial wall thickness is within the range of 0.225 mm to 5 mm.
 5. A heatexchanger according to claim 3, wherein said radial wall thickness isequal to 1.5 mm.
 6. A heat exchanger according to claim 3, wherein saidtransverse wall thickness is within the range of 0.15 mm to 3 mm.
 7. Aheat exchanger according to claim 3, wherein said transverse wallthickness is equal to 0.35 mm.
 8. A heat exchanger according to claim 2,wherein said extruded tubes comprise a number of ribs between 2 and 12,each rib having a thickness within the range of 0.15 mm and 3 mm.
 9. Aheat exchanger according to claim 8, wherein the number of ribs is 3,and wherein the thickness of each rib is 0.35 mm.
 10. A heat exchangeraccording to claim 2, wherein said extruded tubes are located at bothends of said beam.
 11. A heat exchanger according to claim 2, furthercomprising at least one baffle located between two openings of saidtank, wherein said tubes received in these two openings are extrudedtubes.
 12. A heat exchanger according to claim 3, further comprising atleast one baffle located between two openings of said tank, wherein saidextruded tubes comprise a number of ribs between 2 and 12, each ribhaving a thickness within the range of 0.15 mm and 3 mm, said extrudedtubes are located at both ends of said beam, and said tubes received inthe two openings of said tank are extruded tubes.